Lens and process of making the same



5 Oct. 29, 1946. R. F. BAR-DWELL ETAL 1 5 LENS AND PROCESS OF MAKING THE SAME Original Filed 001;. 11, 1959 Sheets-Sheet l INVENTORS RFILPH 'fi BHR'OWELL BY JOHN H. IT'H ATT RNE Oct.-2 9, 1946.? R. F. BARDWE LL ETAL 2,410,145

LENS AND PROCESS OF MAKING THE SAME Original Filed 00%. 11 1939 4 Sheets-Sheet 2 INVENTORS nnLPH r. annovwnz.

gay-av H. .sMI-rH O 9 'R. F.. BARDWELL ETAL 10, I LENS AND PROCESS OF MAKING THE SAME Original Filed Oct. 11, 1939 4 Sheets-Sheet 3 INVENTORS 2 2 l I RALPH F. BHRDWCLL dOHN H. SMITH Oct.29,1946. R g L Em 2,410,145

vLE NS ANIT) PROCESS OF MAKING THE SAME Original Filed Oct. 11, 1939 4 Sheets-Sheet 4.

v INVENTORS RRLPH F. snRawgLL BY JOHN H. s MlTH Patented Oct. 29, 1946 2,410,145 I LENS AND esoonss OF MAKING T n;

Ralph F. Bardwell, S outhbridge, and John H. "Sinith, Taimton, Mass, 'assignors to. American.

- Optical company,

6 Claims- 1 This invention relates to improvements in multifocal or bifocal lenses and to new and improved processes of making the same. The principal object of this invention is to provide an improved one-piec multifocal lens with wide or broad focal fields and with the optical center of "each field in a controlled position, and means and method of making same. r

This is a division of my co-pending application Serial No. 299,006 filed October 11, 1939;

Another object of the invention is to provide a lens of this character of one piece of lens medium having wide or broad focal fields with the optical centers of the different fields calculatedly positioned relative to eachother to prevent jump or displacement, when desired in going from one field to the other and to give the desired relationship of said centers. l

Another object of the invention is to provide new and improved processes for making such lenses in a more economical way and thus reducing the cost of production thereof and the cost to the consumer.

Another object of the invention isto provide new and improved processes of making such lenses wherein some at least of the lens sur aces may be produced on several lens blanks at once, insteadof each surface of'eacn'blan'k being generated separately as has been the past "practice in the art.

Another of the objects of the invention is to provide new and improved processes of making such lenses wherein certain of the operations may be economically performed by molding instead 9? e mor e e s e n in n polishing o erations as is the present practice in the art,

Another object is to provide means for forming, on a single lens of the character described, a plurality of surfaces withoutreblocking the lens.

Another object is to provide a one piece tri rocal lens of the character described in which one sur ace is monax l, With ea of wo s riew which are set monaxial with each other. 7

Another object is to provide "a onepiece trifocalof the-character described in which two of the surfaces are monaxial and two of the surfaces may be formedwithout rehlocking.

Another object is to provide a onepiece trifocal of the character described, in which one surface is monaxial with each of two surfaces Southbridge, Mass, a voluntary association of Massachusetts Original application October 11, 1939, Serial No. 299,0;(16- Divided'and this application January 4g, 134 3 Serial No. 471,248

1. new

2 may be f rm at any desi d angle with. he ad jacent lens surfaces.

Another object is to provide a onepiece multifocal lens of the character described in which the optical centers of each field may be positioned in any desired position independently ofthe other Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying have been shown and described by way Of illustration only.

Referring to the drawings: Y

Fig, I is a front view of a lens of the invention; Fig. II is a cross section on line, II-II of Fig. I; Fig. III is a cross section taken on lineIII -III of ig. I Fig. IV is a front view of a lens of the invention showing the optical centers. of its two fields separated;

Fig.V is a diagrammatic cross section of alens of the invention similar to Fig. III and showing the centering of its fields;

Fig VIis a perspective vlew of a molded blank for making thelens o'fthe invention Fi'g. VII is a perspective viewof the blank illustrating the completion of the distance field;

Fig, VIII is a perspective view of the-blank illustrating' the completion of the readingiffiieldy" Fig; I2; is a par-tialbross'section of a grinding an'dpolishing rnachine on-which the distance field of the lens is groundand polished;

Fig. is a plan view at a lens holder for holdingthe blanks when the distance field 'isgener.

Fig. 251 is a cross section taken on line XIXI Fig.

. "m new on when as feel n ced e grat d Fig. XIIIis a partial side eievation ofFigi XII; 7 Fig. gnv'isa view similar to that of rig. XII, i us th Pew-veins neo ram rr a ape or se ting he ans. 9 th s 'eirsdpi ting radius;

ra u ser e;

' Fi -XV is anema se viswjef ee ti eee the XVI is a pa tia iew intense 1 3a.

I is a partial elevation of a lens grindi separated by the straight division line 3.

3 XVI of Fig. XIV with the gauge removed and looking in the direction of the arrows;

Fig. XVII is a perspective view of an alternate structure of the lens of the invention;

Fig. XVIII --is a central sectional view of the lens of Fig. XVII, showing one arrangement for centering of its fields;

Fig. XIX is a view similar to Fig, XVIII, showing another arrangement of the centering of the fields;

Fig. XX is a view of a lens holder used in the forming of a lens of the type shown in Fig. XVII; and

Fig. XXI is a view similar to Fig. XX, with the holder in position for grindinga different field.

Lenses of one piece of lens material having two or more focal fields ground and polished thereon are very important in the art. The optical crown glass of which they are made is very stable and the best lens medium known for lenses generally. The glass is stable, it does not corrode, and there is an absence of chemical changes, dispersion and color troubles, and difiiculties of expansion, such as are present in lenses made of two or more pieces of different glasses.

Such lenses however have been difficult and expensive to grind, and the proper relationship of the op tical centers of the various fields has been particularly difiicult and expensive to obtain. Due.

to these difficulties and the expense involved fused lenses wherein two or more pieces of different glasses are fused together have come into vogue. These lenses are subject to chemical change and tarnish, there are color troubles due to differences in dispersion and the lenses are liable to crack or separate because of the difference of expansion of the separate parts. It is therefore one of the prime objectsof our invention to provide a one-piece lens of multiple fields having desired broad focal fields, and proper re- V lationshipof the optical centers that can be more economically produced than present day onepiece multifocal lenses.

Referring to the drawings wherein similar.

reference characters represent similar parts throughout:

A lens of our invention is shown in Fig. I. The

' upper or distance field is shown at I, the lower or reading field is shown at 2. The two fields are The fields I and 2 merge together substantially without shoulder'adjacent the center of the lens at 4, thus causing the line 3 to substantially disap- There is a shoulder wards the outer edges. It will be noted that the reading field 2 is a wide field extending entirely across the lens. The optical center 6 is the optical center of both field l andfield 2. The dotted line 1 indicates the pupil of the eye. In Fig. IV.

the optical center 8 of the distance field I, and the optical center 9 of the reading field 2 are shown separated by an amount substantially equal to half the diameter of the pupil of the eye above and below the line 3a which, dueto the separation of the optical centers, is a continuous line, less visible adjacent the center and having a dip 4| whichvaries in extent according to the curvatures of surfaces! and2. The pupil of the eye is indicated by the dotted lines I. The advantage of this centering is that as soon as the eye is clear of the dividing line 3a in either direction it is centered overthe optical center of point of best vision in any lens.

In Fig. V is shown the centering of th surfaces. The surface It of the field l is centered at H, the surface !2 of the field 2 at I3. The centers H and 13 are on the line l4, passing 6 through the line of division 3 of the two fields for the centering shown in Fig. I, To obtain the centering shown in Fig. IV, the center i l is moved up to the point I5, and the center l3 moved down to the point I6; The distance between centers is indicated at 11. This distance may be varied as desired within practicable limits.

The lens is completed by putting on the prescription surface 18 on the side opposite the surfaces IO and [2. This surface [8 is centered as required to give the required powers in the fields l and '2, and preferably ground and polished. The surface 18 is placed at a position to give the re -quired thickness of lens. The surfaces to, IE and I8 are all good optical surfaces. The surface I8 maybe put on at any desired angular relation to the surfaces and I2. I

l The finished lens is characterized by wide focal fields extending entirely across the lens and optical centers placed in controlled relation with each other, thus producing a lens of fine optical qualities.

To produce our lens we proceed as follows:

We mold a lens blank of optical crown glass or other desired lens medium to the shape substantially as shown in Fig. VI. This blank has the field l, the field 2, the division line 3 between the fields, and the shoulders 5. It should be noted that the ridge producing the division line 3 is not absolutely essential. The purpose of this ridge is to'decrease subsequent and/or unnecessary grinding. The blank is of thickness sufficient for the production of a finished lens therefrom, The curvatures of the surfaces l and 2 are approximately those of the finished surf-aces to be ground and polished thereon.

We next mount a plurality of these lens blanks, all of substantially the same curvature and thickness on a lens holder [9, see Figs. X and XI, the blanks'being held in place thereon by the ordinarylpitch blocking or other suitable means.

In Fig. X, three such blanks are shown mounted on the holder l9. The number of-blanks that can be mounted on the holder depends upon the size of the holder and the grinding lap to be used, the flatter the curvature of the surfaces to be round, the more blanks can be accommodated.

When the blanks have been mounted on the holder. is we place the holder in place on the grinding lap 25 of the grinding machine shown in FignIX. The lap 20 is rotated by the shaft 21, and belt 22. The crank pin'23 of the upper spindle 24 of the machine is placed in the recess 25 of the holder 59. The spindle 24 is rotated by the belt. 2%. The holder l9 travels over the lap 29, being carried around by the crank 21,

causing a break up motionon the grinding surface to prevent concentric rings and scratches and insuring a smooth surface being generated.

We grind and polish the surface of the field l in this manner. It will be noted that in this way we are able to work on a plurality of lenses at the same time and to use standard methods of grinding and polishing. This results in great economy. When the surface of field I is thus ground down it will extend somewhat into the surface of 'field 2 as indicated by arcuate line 28 in Fig. VII.

We then remove the blanks from the holder I9 and mount'the blanks singly on a holder 29,

' VIII.

"its upper end and" has a handle 55 for adjustings ea. 7 I 38 is eccentrically mounted at '31 on the wheel I V '75 In order to produce 1 the desired angle relative to the adjacent'surfaces of the lens, the edge of the tool 32vis beveled, as

shown at 52 in Fig. 2G1. This beveling makes it possible to tilt the tool sidewaysto bring its edge i2 to any desired point on the'lensfi It will be readily understood that, if an exact right angled clifi edge is desired, the angle of the bevel necessary at different tilted positions will vary. However, since the angle of the cliff edge may readily be conceived to be more effective at other than a right angle to achieve certain results such as diminishing of reflections, it has been found, that for practical purposes, one angle of the tool edge will produce, at different tilted positions, practical cliff angles within a considerable range, with the departure from right angularity being substantially negligible. It is to be understood, also that greater departures from right angularity of the cliff edge may be accomplished, when desired, by properly angling the tool edge, while taking into consideration the amount of tilting of'the tool. The tool 32 is carried by the spindle 33, rotated bythe flexible shaft The spindle is pivotably movable about the axis 35. The holder 29 is oscillated back and forth about the axis 35a in such away as to carry the ring tool over the surface of field 2 in a direction substantially parallel with the line 3, see Fig.

The grinding and polishing operations are done swingable U-shaped lens holder support 45 pivoted thereon to swing'about the axis 35a. An

The dotted lines 36 indicate the outline of the tool 32.

upright support member 6'6 is positioned sub stantially centrally of the yoke-likeme'mber 44 along the axis 35a, and to one side thereof, and

ing id of the yoke 44.

On the outer end of the arm Ll? is a shaft ti on which is mounteda slidable weight .52, held in adjusted position by ascrew 53."

5" adapted to 'engage'depressions E8 on thefaces E9. 4

i are used to determine lens holder 29.

6 support about the axis 35a. In order to prevent line scratching in the work during abrading it is necessary to provide a break up action when grinding lenses. The break up motion in this instance accomplished by a Geneva type pickup mounted on the pivot 37, having pickup spokes 58 for engagement with a stationary pin 59:; so that the swing of the support d5 about the axis- 35a is varied in length at each revolution of the wheel 57, due to the movement of the cam 5% which is moved to a different position each time one of the spokes '58 is moved by the tripping action against the pin 59a. R

It will thus be seen that the less holder 29 is oscillated by theeccentric crank 31 and connecting rod 33 mechanism, and is rotatably. adjustable to align the cliff edge in right angled relation with the trunnion axis 35a, as well as being longitudinally adjustableand resiliently held against the lens by spring 43.

t will be noted that when the surface of the field 2 has been completed the line 28, Fig. VII, has substantially disappeared, and that the surfaces of field l and 2 have merged on the line 3 adjacent the center and have the shoulder 5 between them towards the outer edges. It is to understood that the axes35, sea, and the longitudinal axis of the tool, preferably meet at a common point, L

In Figures XIV, XV and XVI is illustrated a gauge and its operation in setting the lens holder 29 of Fig. XII to the proper height. The gauge "H consists of a horizontal bar 59 and a vertical bar 56 adjustable transversely thereof. These cross bars, in combination with a testblock iii, theproper position for the The bar 59 has a hollow portion 'i'z 'which cc-ntains a spring 63. A free end '64 slides inthe hollow .EZagainst the-action of the spring fid'so as 'to be urged outwardl, and is held therein by a pin 65 fixed in the bar 59 and extending into a slo-tfid in the free end 6 5. The points are of thesupport'tt. These depressionsse are centered on the aXis 3511. There is a scale calito, curvature to be ground.

bratedto suit the convenience of theoper'ator, on the bar (it. The test block iii is'formed te'the The procedure followed in grinding the reading portion of the lens is, then, asfollows: The gauge "TI is snapped into position on :the support 55, as

The support ts carries a shaft 3%! in a bushing I The shaft 3%} carriesthe lens holder 29 on 5? may be loosened to allow the shaft 33 "to be, rotated so as to position the line 3 on the lens" in desired relation with the tool edge and in substantial parallelism with the axis 35.

" f'l hesupportfi'd'is oscillated'about the aXis.35a by means of a connecting rod 38, which ispivotally'attached to the support 45, preferably cen 'tral'ly thereof as lildlCatdiIl'Flg'XIII so as to provide substantially equal thrust on the beat- The other end of the connecting rod 51 to provide the "back and forth drive ofthe shown in Fig. fiV, with the bar til adjusted to the radiusof the curvature to be'greund on the lens. A test" block 6!, having a face formed to the curvature to'be -groundon the lens is placed in position Onthe shai't id as shown in Fig. XIV.

"'The'shaft 30' is then adjusted, by means of the handle 55, untilthe gauge l i may be swung across the surface of the 'test block, or vice versa, with the p'ointll! barely touching the surface.

' e The block 6! and the gauge ii are then removed and the lens holder, with the lens-to be ground thereon, is positioned on the shaft 3d asashown in Fig. XII; and the tool 32 brought into contact with the lens to carry out the grinding operation through the motions previously described.

It is tobe understood that thespindle ss may be moved out of the way to make room'for the 7 the lens, when finished. In other Words, the test block BI is so calculated and the height of the shaft 30 so set in accordance therewith, that, when the surface being ground on the lens is finished, if desired, the gauge, still at the same adjustment when used with the test block, may again be snapped into place in the support 45, and

the point 12 will have the same relation with the finished lens surface as it previously had With the surface of the test block.

It is to be understood that many other mechanisms could readily be devised for the gauging and grinding of any of the surfaces mentioned herein before or after, and that the structures shown and described are shown for the purposes of illustration as one means and method of accomplishing the desired result.

The tool may, if desired, be positioned with. its edge 42 removed from the line 3 of the lens and allowed to feed gradually towards said line 3 as it moves down through the lens. This may be accomplished by setting the screw if in the side arm 41 so as to hold the spindle 3%! in desired angular position relative to the axis 35a, and setting the weight 52 on the shaft 5! to produce the desired pressure of the tool on the lens either in combination with the pressure already exerted by the spring 43, or by itself. The too-l may thus be fed simultaneously int-o and across the lens, if desired.

It is to be understood that the feeding operations involved in forming the lenses of this invention may, if desired, be performed manually, instead of mechanically by the means shown or other suitable means.

Figures XVII through XXI are illustrative of an alternative lens structure and means and method of making the same. It is to be understood that, although a trifocal lens is shown, lenses having more focal fields may be similarly formed. a

In Fig. XVII is shown a blank for a trifocal lens, comparable to the bifocal blank of Fig. VI.

The lens as shown in Figs. XVII and XVIII comprises surfaces "#4, l5 and 16, which may be the;

jump, there must be one point at which the radii distance, intermediate and reading portions respectively or in any other desired order. There may be two distance portions, or two reading portions, or any other desired combination.

The lens is made of one piece of glass, thereby;

on a multiple lens block similar to that shown in;

Fig. X. As in the bifocal lens, and with similar apparatus, each lens is then blocked singly and curve 15 is ground. The radius of curvature is gauged as shown in Fig. XIV and the same procedure followed as in the forming of the bifocallens holder is set to the proper angle with respect to and by pivoting about the axis 35 of the machine of Fig. X11, and the oscillation to the proper radius as previously described, and the same procedure is gone through as for curve l5. Curve [8 is ground until it merges with curve 75 centrally of the line of division 8!.

Surfaces l5 and H3 will not be monaxial although the two curves do merge as described. This gives a condition known to the art as a jump between surfaces and :78. For some purposes this jump is not a sufliciently great disadvantage to make the lens an impractical one, since the lens may be formed inexpensively.

It will readily be seen that, if there is to be no of the two curvatures lie along the same line, and this line must pass through the line of division of the surfaces. As may be seen in Fig. XVIII, the radius of the surface 16, having its center at 82 on the axis l9 passing through the line of division 80 between the surfaces I 1 and 15, has only oneposition in which it may lie along the same line as the radius of the surface 15 which has its center at Hi, and that is along the axis '59. Since this axis does not pass through the line of division M, the surfaces 15 and 16 may merge, but will not be monaxial.

The final result in forming the lens as illustrated in Figs. XVII and XVIII is a lens of one piece of glass, which, if a trifocal of the usual type is desired, will have three powers controlled in part by the surfaces 14, 15 and 16, which is free from color and'all'of the focal fields of which extend across the entire width of the lens. Surfaces 14 and 15 will be monaxial or jump-free. Surfaces l5 and 16 will merge at a point on their line of division 8], preferably centrally thereof but readily at any other point thereon, but will not be monaxial and will have a slight jump which for some purposes is not impractical. Surfaces I4, 15 and 16 will be of different curvatures thereby giving different powers to the three surfaces. Thesema be any combination of curvatures desired, not necessarily all different.

In Figs. XIX, XX, and XXI is illustrated the forming of of trifocal lens similar to that illustrated in Fig. XVIII, from the same type of blank as shown in Fig. XVII, with the difference that this lens is designed to be "jump free throughout. 7

. have three powers, with surfaces l4, l5 and 16 just as in the previously mentioned trifocal, and

lens previously described in this specification. A's

before, the center of oscillation, that is,the axis 35a is also the center of the curve to be ground. The lens holder is set to a distance from the center of oscillation equal to the radius to be ground,

and as the lens is oscillated across the rotating tool, the correct curve is ground thereon. The radii of the surfaces "M and 15, having their centers at 11 and F8 on the axis '19 passing through their line of joinder 80, willpermit the merging, centrally of the line of division Bil, of the two surfaces 14 and I5 to make them monaxial, as is the bifocal previously mentioned.

The curve 76 is ground in the same manner as the curve 15 without reblocking the'lns. The

the same general advantages and alternatives apply, with the addition that surfaces l5 and 16 as well as 14 and 15, are made monaxial.

The same method of manufacturing is used for grinding and polishing surfaces E4 and E5 as is used in the previously mentioned trifocal. Surface 16 is ground and polished by a method and with apparatus which makes it monaxial with surface 15.

This method consists of blocking the lens on a two piece adjustable lens holder 83, see Figs.

XX and XXI, the upper part 84 having the lens point with the axes 89 and 9G.

9 fits on theshaft all of Fig. XII. The surfaces 15 and '36, are made monaxial by adjusting the upper part 184, to. offset position as shown in Fig. XXI, when the surface 16 is ground, and by setting the grinding or polishing, tool to the proper angle, as was described in connection with the previously mentioned trifocal and bifocal. The slot 85 is. designed so that when the pin 8? is at one end thereof, as in Fig. XX, the len is in proper relation to the tool 32 for the grinding of surface l5, and when the pin is at the other end of the slot the lens is in proper relation to the tool for the grinding of surface l6 so as to make it monaxial with surface it and so as to eliminate fjump between surfaces 15 '56 as well as M and '15. i

In order to make the surfaces 55 and 76 monaxial at the same time that surfaces 14 and 75 are monaxial, the arrangement of centers of curvature of the various surfaces as illustrated in Figs. XIXthrough XXI is necessary. It will be noted that the centers 11 and .'8 both lie on the axis is which passes through the line of division between surfaces M and I5, and that the centers i8 and82 both lie on the axis 89 which passes through the. line of division between surfaces i and IE. r 7 What is done is simply this-when it is desired to form the surface .55, the lens holder is adjusted to bring the axis F9 in alignment with the 9 9 of the lens holder 83 so as to allow the axis 9! of the tool to be al gned at one point with the axes Iii and 99. This makes it possible to form surfaces id and i5 monaxial. The lens holder is again adjusted by means of the slot $5 and pin Bl when it is desired to form the surface '56, so as to bring the axis 83 in alignment with the axis 9% of the lens holder 83 so as to allow the axis ill of the tool'32 to be aligned at one This makes it possible to form surfaces l5 and i5 monaxial. Further surfaces may readily be formed by making possible further adjustments of the lens holder 83.

Having formed one side of the lens, bifocal or trifocal, the prescription surface l8 is next placed on the opposite side of the lens,

This is a surface so formed and so located as to produce the prescription desired in each focal field in combination with the opposing surface. This surface I8 is ground and polished by the ordinary methods of lap grinding.

One form of the finished lens is cut from the blank as indicated by the dotted line 39 in Fig. VIII.

In dispensing these lenses the surfaces In and I2 or l4, l5 and H5 may be placed thereon by the manufacturer and the surface I8 by the dispensing prescription grinder. This insures prompt service to the consumer.

Lenses of this character are very desirable in the art. They have wide focal fields which are of importance in many occupational and other uses. The centering may be made and arranged to best advantage when it is desired to avoid displacement or jump in going from field to field and is exceptionally facile in the positioning of these centers thus overcoming a decided drawback in onepiece multifocal lenses up to date. This may be accomplished by tilting either the tool or lens holder. They may be produced with a decided reduction in cost from present day onepiece multifocal lenses. They lend themselves perfectly to the methods of dispensing lenses now in vogue in the art. The prescription surfaces 10 may be 'applied with equipment and apparatus now in use, hence no investment on thepart of the prescription dispenser is required. I

In Fig. II the shoulders at the sides of the lens are indicated at. 40.

In Fig. V it will be noted that the surface In centered at I I has a shorter radius than the surface I 2 centered at l3. This being so, the surface IEB will cut into the surface l2 along the line 28 as the surface It is ground. This extension however will be substantially ground away when the surface I2 is ground as the surface I2 is fiatter. Flatter surfaces may be ground to merge, at one point at least, with a sharper curved surface. I

,It is to be understood that the term multifocal as used in this specification and accompanying claims is intended to mean lenses having two or more focal fields.

Certain type of curves may bring about a condition in which surfaces merge at a point other than centrally of the line of division between said the ophthalmic art may be formed on the various surfaces described, such as prismatic or other common surfaces, and that the optical centers of the various fields may be calculated to different positions as desired.

From the foregoing it will be seen that we have provided simple, efficient and particularly economical means for obtaining all the objects and advantages of the invention.

Having described our invention, we claim:

1. A blank for a multi-focal lens comprising a single piece of lens medium having on one face thereof at least two lens surfaces constituting two focal fields, each of said surfaces having a spherical. curvature throughout and extending laterally substantially the entire width of the blank and with a substantially straight line of division therebetween and extending the full width of the blank along said line, the radii of curvature of said surfaces being different from each other by an amount sufficient to give the desired difference in focal power between the two fields and the centers of the curvatures of said surfaces being positioned relative to each other so as to cause the said surfaces to meet in substantially flush relation with each other adjacent the central portion of and substantially along the line of division between the two fields with the remainder of said line of division on the opposed sides of said substantially fiush portion being shouldered with the shoulders progressively increasing in height in the direction of the sides of the blank.

2. A multi-focal lens comprising a single piece of lens medium having on one face thereof at least two lens surfaces constituting two focal fields, each of said surfaces having a spherical curvature throughout and extending laterally substantially the entire width of the lens and with a substantially straight line of division therebetween and extending the full width of the lens along said line, the radii of curvature of said surfaces being different from each other by an amount sufficient to give the desired difference in focal power between the two fields and the centers of the curvatures of said surfaces being positioned relative to each other so as to cause the said surfaces to meet in substantially flush relation with each other adjacent the central portion of and substantially along the line of division between the two fields withthe remainder of said line of division on the opposed sides of said substantially flush portion being shouldered with the shoulders progressively increasing in height in the direction of the sides of the lens and a finished optical surface on the opposed face of the lens and of a curvature which when combined with the curves of said first two surfaces will produce the optical powers desired of the focal fields.

3. A blank for a multi-focal lens comprising a single piece of lens medium having on one face thereof at least two lens surfaces constituting two focal fields, each of said surfaces having a spherical curvature throughout and extending laterally substantially the entire width of the blank and with a substantially straight line of division therebetween and extending the full width of th blank along said line, the radii of curvature of said surfaces being different from each other by an amount sufficient to give the desired difference in focal power between the two fields and the centers of the curvatures of said surfaces both lying on a line passing through the line of division so as to cause the said surfaces to meet in substantially fiush relation with each other adjacent the central portion of and substantially along the line of division between the two fields with the remainder of said line of division on the opposed sides of said substantially flush portion being shouldered with the shoulders progressively increasing in height in the direction of the sides of the blank.

4. A multi-focal lens comprising a single piece of lens medium having on one face thereof at least two lens surfaces constituting two focal fields, each of said surfaces having a spherical curvature throughout and extending laterally substantially the entire width of the lens and with a substantially straight line of division therebetween and extending the full width of the lens along said line, the radii of curvature of said surfaces being different from each other by an amount sufficient to give the desired difference in focal power between the two fields and the centers of the curvatures of said surfaces both lying on a line passing through the line of division so as to cause the said surfaces to meet in substantially flush relation with each other adjacent the central portion of and substantially along the line of division between the two fields with th remainder of said line of division on the opposed sides of said substantially flush portion being shouldered with the shoulders progressively increasing in height in the direction of the sides of the lens and a finished optical surface on the opposed face of the lens and of a curvature which when combined with the curves of said first two surfaces will produce the optical powers desired of the focal fields.

5. A blank for a multi-focal lens comprising a single piece of lens medium having on one face thereof at least two lens surfaces constituting two focal fields, each of said surfaces having a spherical curvature throughout and extending laterally substantially the entire width of the blank and with a substantially straight line of division therebetween and extending the full width of the blank along said line, the radii of curvature of said surfaces being different from each other by an amount sufficient to give the desired difference in focal power between th two fields, the center of curvature of one of said surfaces being offset to one side of a line passing through the said line of division an amount substantially equal to half the diameter of the pupil ofthe eye and the center of curvature of the other of said surfaces being ofiset to the opposed side of said line passing through the line of division an amount substantially equal to half the diameter of the pupil of the eye with the said surfaces meeting in substantially flush relation with each other adjacent the central portion of and substantially along the line of division between the two fields with the remainder of said line of division on the opposed sides of said substantially flush portion being shouldered with the shoulders rogressively increasing in height in the direction of the sides of the blank.

6. A multi-focal lens comprising a single piece of lens medium having on one face thereof at least two lens surfaces constituting two focal fields, each of said surfaces having a spherical curvature throughout and extending laterally substantially the entire width of the lens and with a substantially straight line of division therebetween and extending the full width of the lens along said line, the radii of curvature of said surfaces being different from each other by an amount sufficient to give the desired difference in focal power between the two fields, the center of curvatur of one of said surfaces being offset to one side of a line passing through the said line of division an amount substantially equal to half the diameter of the pupil of the eye and the center of curvature of the other of said surfaces being offset to the opposed side of said line passing through the line of division an amount substantially equal to half the diameter of the pupil of the eye with the said surfaces meeting in substantially flush relation with each other'adjacent the central portion of and substantially along the line of division between the two fields with the remainder of said line of division on the opposed sides of said substantially flush portion being shouldered with the shoulders progressively increasing in height in the direction of the sides of the lens and a finished optical surface on the opposed face of the lens and of a curvature which when combined with the curves of said first two surfaces will produce the optical powers desired of the focal fields.

RALPH F. BARDWELL. JOHN H. SMITH. 

